A message from the Director-General

I am very glad to be able to contribute this introduction to the first CERN COURIER of 1962. We have been without our journal for quite a long time, but we can now look forward to seeing it regularly again once a month. CERN COURIER is an important publication of ours, because not only does it serve to link together all members of the Organization, and their families, but it also has a strong part to play in showing CERN to the member States and to other parts of the world.

This institution is remarkable in two ways: It is a place where the most fantastic experiments are carried out. It is a place where international co-operation actually exists. These two statements call for some explanation: It is difficult to appreciate the full significance of an activity if all one's energy is devoted to it. The everyday work accomplished at CERN Message from the Director- hides its real importance, the tremendous impact of what is going on General 2 here. What I am tempted to call the 'romantic glory' of our work is over­ looked. But you must never forget that in the PS, at the moment when Last year at CERN 3 the beam hits a target, at the moment when matter undergoes a transfer Radiation safety at CERN . . 4 of energy, you have created conditions which probably do not exist Johan Baarli 8 anywhere else in the universe, not even in the explosions of super-nova stars. What an opportunity to penetrate the innermost structure of matter CERN theoretical conference . 9 in conditions never created even by Nature ! 50th anniversary of the Solvay But CERN is also a centre of international co-operation, unique of its Physics Meeting 10 kind. There are other examples of such co-operation in economic, politi­ They worked at CERN .... 10 cal, and military fields. But all our work is for an idealistic aim, for pure science without commercial or any other interests. Our effort is a symbol 19th session of CERN Council . 13 of what science really means, namely the exploration of Nature by Man. Nuclear-emulsion work at Here, differences based on nationalities are non-existent. And, in this CERN 14 respect, CERN is the only really scientific laboratory, because it is international. CERN is now passing from the first period, of machine construction, The cover photograph shows ihe large to the second, the period of scientific research with the machines. The electrostatic separator, the second of a first period has been a heroic one. CERN has accomplished an incredible series of three built by the NPA Division, task which is outstanding in the history of accelerators. Many people installed in the South experimental hall thought Europe would never be capable of such an effort. In fact of the synchrotron. In ihe background are a portable radiation barrier and con­ Europe managed it even better than others. crete shielding (an article on radiation We now possess two of the best accelerators in the world. One, the safety begins on p. 4). PS machine, which, together with the Brookhaven accelerator in the Photo credits: all photos by CERN/PIO, U.S.A., is the largest machine in the world ; the other, the SC machine except p. 11: Couprie, Brussels. which is smaller but still an extremely useful tool of research. We must do our best to exploit these machines for scientific dis­ coveries. For this purpose many large instruments have to be built. We CERN COURIER need bubble chambers, separators, beam transport equipment, and many is published monthly in English and in other things which have still to be built. French. It is distributed free of charge to At the same time, we are beginning to perform experiments, and to CERN employees, and others interested discover new phenomena and new facts of nature. The work at CERN in the construction and use of particle has already contributed much to the knowledge of the structure of the accelerators or in the progress of nuc­ elementary particles which make up atoms. If we are successful, the next lear physics in general. few years at CERN will be most interesting and exciting. The beams of The text of any article may be reprint­ the accelerators at CERN penetrate the innermost parts of the atom. ed if credit is given to CERN COURIER CERN therefore presents a unique opportunity to the physicists of Copies of most illustrations are avail­ Europe for solving some of the most important questions: What is the able to editors, without charge. structure of the proton and the neutron ; what are the constituents of Published by the atomic nuclei; what is the nature of the nuclear force which keeps them European Organization for together and which is the cause of nuclear energy ; what is the secret of radioactivity ; and what are the properties of anti-matter ? Nuclear Research (CERN) All these questions and many others are under study here, in inter­ PUBLIC INFORMATION OFFICE national collaboration: fourteen nations are exploring the unknown. Roger Anthoine Editor: Alec G. Hester CERN, Geneva 23, Switzerland Tel.: 34 20 50 Printed in Switzerland 2 BRINGING THE RECORD UP TO DATE Last year at CERN

Owing to the long time since the last appearance of CERN control desk was installed in August, and a platform erected COURIER, our usual feature 'Last month at CERN' requires a in the North hall to act as a centre for counting and control temporary change of title. Unfortunately it is not possible equipment belonging to the experiments. The accelerator to cover in detail all the events of the past year, but if is can now produce secondary beams of 120-milliseconds hoped that the following account includes the chief items of duration, and a 6-headed target assembly is also being interest and gives an idea of what has been happening used with success. recently at CERN. In June, there were altogether 44 standard magnets and From the beginning of the year, the laboratory was lenses available for the guidance of secondary beams from reorganized infernally into twelve divisions, indicative of its the PS. To supply them with power the new generator broadened scope and increased emphasis on experimental building houses 30 generators with outputs ranging from 40 work, following the full operation of the second particle to 320 kW together with 4 of 1500 kW each. accelerator. The divisions are : PS Machine, SC Machine, In the first ten months of 1961 the synchro-cyclotron Nuclear Physics, Engineering, Data Handling, Theory, Track provided 5361 hours operating time for nuclear physics, Chambers, Nuclear Physics Apparatus, Accelerator Research, apart from over 1000 hours when 'parasite' experiments Site and Buildings, Finance, and General Administration. Then were possible. In this time only 195 hours were lost because on 1 August, J. B. Adams left for England, to be replaced as of machine faults. In addition to the Easter holiday, Director-General by Prof. V. F. Weisskopf. The 19th Session there was one shut-down of 10 days in mid June and of the Council, reported briefly elsewhere in this issue, took another in October. place at CERN on 2 June, and the 20th on 19 December. The internal beam intensity was raised during the year A noticeable change has been brought about in the from 0,3 to 0,8 \xA, by mixing small amounts of argon in appearance of the site by the progress on new building the hydrogen supply to the ion source, and improving the projects. In April, 1120 m2 of floor was laid in the courtyard electrostatic focusing near the source. Another way of at the eastern end of the South experimental hall of the increasing the usefulness of this accelerator has been the proton synchrotron, followed two months later by roofing, installation of devices designed to increase the duty ratio thus providing another large area for engineering and of infernally produced secondary beams. An increase from auxiliary experimental work. A further wing was added to below 1 % to about 25% is achieved. Further studies and the adjacent laboratory block. One result of these changes experiments are continuing to augment the intensify and was to enable the Engineering Division to release the space improve the duty ratio of the extracted proton beam. Twelve it formerly occupied in the South hall. For the new East new generators of a total capacity of 680 kW have been experimental area the large triangular apron has been laid installed to supply beam transport equipment. and the new building at the end of it has already started to Among activities in the Engineering Division, two proto­ receive sections of the 1,5 m British Hydrogen Bubble types of controlled semi-conductor rectifiers were built, one Chamber. The neighbouring compressor and generator rated at 500 A, 125 V, the other at 100 A, 25 V. Such buildings to serve this and the CERN 2-m hydrogen bubble rectifiers, used instead of motor-generator sets, will simplify chamber that will also be installed, are more or less finished, the provision of power for beam-transport magnets. Other and at the end of the year a 10-m-diameter steel sphere was applications of semi-conductors, developed by the Nuclear being completed at one corner of the apron. This is to Physics Division, are transistorized scalers, fast pulse ampli­ accept in the form of gas the whole volume of hydrogen fiers, etc. from either chamber in case of emergency. Still on the subject of new equipment, the magnet The NPA building, for development of nuclear physics armature for the CERN 2-m hydrogen bubble chamber was apparatus was brought info operation in June, and parts of completed at the manufacturers' works towards the end of the new building for the Accelerator Research Division in the year. Also nearing completion was the transport system : December. On 6 November, new electrical and mechanical on site, the 4000-W refrigeration system was being erected. stores for the Site & Buildings Division were inaugurated. Development of the microwave particle separator has An important step forward in the use of the proton continued, the aim being to produce separated beams of synchrotron was the bringing into service of the North antiprofons and positive and negative kaons between 10 experimental hall in September. Towards the end of the and 20 GeV/c. Experimental equipment to permit the year, the first of the CERN electrostatic separators was accurate study of spark-chamber operation was completed. installed there as part of the system for providing a 1,5 A major success of the year was the setting up of the GeV/c negative K-meson beam. The electrostatic field of separated antiproton beam (up to 1 GeV/c momentum) from this separator can be as high as 53 kV/cm over a gap of 8,5 the PS. This was carried out by the Nuclear Physics Division cm. The 32-cm hydrogen bubble chamber operated by the with the assistance of visitors, and was made possible by Track Chambers Division was transferred to the North hall the use of two electrostatic separators from the University of initially to help in setting up the beam and then for Padua. In addition, a score of lenses and magnets were experiments. The d.c. power supplies in this hall total 3500 used to guide the beam, fed by 18 independent generators. kW for beam-transport magnets and 3000 kW for track- The first experiment using the 81-cm hydrogen bubble chamber magnets. chamber from Saclay was carried out with this beam, result­ Full exploitation of the synchrotron was hampered to ing in 170 000 photographs showing 300 000 antiprofons some extent by the civil engineering work on the East stopping in the chamber, and another 90 000 photographs junction, and for some time it was possible to run the showing low-energy antiprofons passing through. A study is machine only at week ends. Complete shut-downs totalling being made of the production of pairs of K-mesons by 11 weeks were also necessitated by this work, by the antiprofons at rest. Measurements of total cross-section in installation of new equipment, and for changing beams. hydrogen have also been made. In September, this beam More time was lost by the breakdown of parts of the was replaced by its successor, designed for separated injector system. In spite of these pauses, however, some antiprofons up to a maximum of 6 GeV/c. With the second 1540 hours were devoted to nuclear physics in the six of the CERN electrostatic separators installed in the South months from June to November, out of a total running time PS hall, 3,6 GeV/c was reached in December. of 1907 hours, and at the end of the year 93 hours a week If is not possible to note all the dozens of experiments were being given to nuclear experiments. Beam intensity that were carried out during the year. We should mention then was 2,5 X 10" protons per pulse. The permanent PS (continued on p. 12)

3 In this article, adapted from a paper which he read at the IVe Conference Internationale Radiation Safety de Protection Civile, at Montreux, last Octo­ ber, Dr. Baarli describes the means adopted at CERN to ensure safety from radiation haz­ at CERN ards, and how effective they are. A previous article by Bernard M. Wheatley fCERN COURIER No. 13-14, Aug.-Sept. 1960) dealt more fully with the Health Physics Group by Johan Baarli, Head of Health Physics itself.

During the design of the CERN It is also a general rule that nobody accelerators theoretical studies were Most danger arises when ma­ is allowed to enter the experimental carried out in order to determine the chines are operating, but heavy halls unless the beam holes are plug­ shielding and restricted access en­ specifications of the necessary shield­ ged. If, however, radiation survey sure safety. Main hazard is given measurements result in tolerable ing arrangements. Shielding is of by fast and slow neutrons — apart importance for two major reasons: to from external beams, which are dose-rates, even with the holes open, reduce the radiation level around the made inaccessible. Prediction of access is given according to the re­ machines in order to carry out ex­ actual beam hazards is difficult be­ sults obtained. On this point it is of periments under conditions which cause of scarce data on biological interest to mention that CERN fol­ are as 'clean' as possible, and to give effects of particles with GeV lows the rules and regulations set general protection against radiation. energy. Neutron intensify outside forth by the International Commission PS shielding but within safety fence The results of these calculations have on Radiological Protection (ICRP). is 5% of maximum permissible to a large extent determined the level (2.5 mrem/h) for continuous The radiation safety during opera­ shielding dimensions and arrange­ exposure, in plane of beam ; rather tion of the synchro-cyclotron can be ments now forming part of the ma­ more than m.p.l. near ventilators. judged from dose measurements - chines. Measurements in general site area made just outside the main shielding. Radiation safety at the CERN site show neutron level only few times Such measurements have shown that background with both machines falls into two major categories accord­ the major part of the radiation level operating. ing to whether the machines are is caused by fast and slow neutrons. Hazard with machines shut down However, the level is low during operating or not. During usual opera­ is local, mainly beta and gamma normal operating conditions, and can tion of either machine the accelera­ radiation from iron in vacuum tank. tion of protons takes place in the Levels of 6 rem/h in vacuum tank only be detected with some accuracy vacuum chamber, which is completely to 10 mrem/h in machine hall have using neutron counters and nuclear- surrounded by the radiation-shield­ been measured for SC ; 2 rem/h track emulsions. Values obtained ing arrangements. The beam of ac­ near targets for PS. using these kinds of instrument show celerated protons then hits a target — 800 people out of 1400 wear dose rates on an average well below gamma film badges; located in the vacuum chamber. Scat­ 10°/o of the maximum permissible — 150 also wear neutron film level of 2.5 mrem per hour * for 40 tered protons, or particles produced badges. hours a week. Although this infor­ by nuclear reactions in the target — All 800 have medical inspec­ material, pass out of the vacuum tion at least once a year. mation is based on calibration with chamber, are collimated through In 1960, 703 received less than 1/5 polonium-beryllium neutron sources, holes in the shielding, and are used for maximum permissible exposure of and as such would require a similar experiments in the halls located out­ 5 rem; only 1 slightly above. spectral distribution of neutrons for side. Under these circumstances the accurate measurement, it is believed radiation outside the shielding is kept that the values cannot be far out. low, although there is still a certain General radiation-safety problems, This view is supported by the good radiation level outside due to some apart from those closely concerned agreement between values obtained penetration. This radiation is mainly with the machines, are also met at with different kinds of instruments composed of fast charged and un­ CERN in connexion with the use of used for the same measurements. charged particles and offers special radioactive sources for calibration In the regions outside the walls of problems for measurements of radia­ and testing purposes, and also in the experimental halls the radiation tion dose and judgement of radiation connexion with irradiated targets level varies greatly according to the hazards. taken out and used for nuclear chem­ kind and number of experiments During shut-down of the machines, istry studies. In addition, there is which are carried out at any parti­ radiation-safety problems are mainly the control of radiation-exposed per­ cular time. This makes the prediction caused by induced radioactivity in sonnel, which forms an important of radiation safety for these regions the targets and in the materials of part of the CERN radiation-safety quite difficult. However, shielding the vacuum chamber and surround­ activities. barriers of movable concrete blocks ing machine components. Particles along the outside of the walls reduce accelerated to high energy cause nuc­ Safety during operation the radiation level in these regions lear reactions which result in radio­ Fig. 1 shows a plan of the 600 MeV also to values of the order of a few active nuclei of great variety. Prob­ synchro-cyclotron (SC) with the percent of the permissible level. lems of radiation safety in this con­ vacuum chamber, the target, magnet, It remains to be mentioned that the nexion are quite similar to those met shielding walls, and experimental whole accelerator, together with the when working with radioactive iso­ halls. Beams of fast particles pro­ topes, the difference being that the duced in the target are taken out into radioactivity is here concentrated in the experimental halls through chan­ * mrem is the abbreviation for millirem, the machine components and mate­ nels in the shielding. The radiation or one-thousandth of a rem, and is a measure of the effect of any form of rials that the beams have been hit­ level inside the machine hall is quite ionizing radiation on human beings. The ting. This necessitates special pre­ high when the machine is operating, rem is obtained by measuring the amount of radiation in rads and multiplying by cautions for work near the machines, and a very reliable security system an appropriate factor of relative biological and for maintenance and repair of the ensures that nobody is left inside or efficiency. For x-rays, the rem, the rad, and the roentgen are approximately the machines themselves. can enter this region at such times. same.

4 people live and move around, the amount of radiation they meet changes; sometimes more, sometimes less. Thus, providing What is the amount of man-made radiation and the number of people subjected to it are together kept below a certain level, it is impossible to detect any difference in the overall health of the Radiation Safety? population. These permissible levels of radiation of different sorts, and Most readers will know that nuclear radiations are 'danger­ various other rules for the safe use of radiations, have now ous', which really means that appropriate care is necessary been generally established by law, based on the recommenda­ whenever or wherever they may be present. Even this perhaps tions of such bodies as the International Commission on needs qualifying, since long before men learned to use nuclear Radiological Protection, which has brought together specialists energy they lived in a 'background' of nuclear radiations, in relevant fields from many countries since 1928. coming from outer space above and the soil beneath. Any source of nuclear radiations has to be constructed or Nobody knows exactly what damage radiation will do to the used in such a way that no significant amount of radiation is human body. A large amount of radiation will cause death, it produced by it in areas open to the general public. The people is true, but as the intensity is reduced it becomes more and working with it are allowed a higher dose, because they form more impossible to predict precisely what will happen. A given a relatively small group of the population and the amount of amount of radiation may or may not have noticeable effects. radiation they actually receive can be measured. Various ins­ One is in a position to say that if 100 people were accidentally truments are used to detect the different types of radiation and exposed to a large amount of radiation then in a certain case to measure their intensities, to show how safe any particular area 10 of them would become ill, but one could still not say just is. In addition, a small piece of special photographic film is worn which 10 that would be, or even whether the number would be by every person likely to be exposed to the radiation, the 9 or 11. Certainly all 100 would not be affected in the same blackening of this film when developed after a certain time way. The genetic effects, that is the possible damage to their indicating the amount of radiation absorbed in that period. future children, would be even more difficult to predict in a More directly, special dosimeters can be worn, if necessary, to precise manner. One can only estimate the chance of any partic show at once the accumulation of the dose. ular result. The smaller the amount of radiation received the Generally, the intensity of the radiation is reduced by smaller is the chance that any damage will be caused, and this absorbing it in suitable material, such as lead, concrete or gives the clue to the way in which radiation can be used safely. earth, or just in air over a greater distance. The difficulty of It has already been mentioned that we have always lived the shielding problem depends, of course, on the original with a certain amount of radiation, but this amount is not intensity ; with accelerators like those at CERN it is easier constant. There are more neutrons in the air on top of a moun­ than with a large nuclear reactor for electric power production, tain than there are in the valley, for example ; rocks and soil, for instance. The biological effect of the radiations also depends and indeed bricks for houses, in some parts of the world are more or less on the total amount absorbed, so that in cases more radioactive than in others ; disturbances on the sun can where it is not possible to reduce the intensity further, safety change the intensity of the cosmic rays hitting the earth. As can be retained by limiting the time of exposure.

experimental halls, is surrounded at tor, which is essentially a 50-MeV The whole ring-shaped accelerator some distance by a fence, inside linear accelerator, provides protons is completely surrounded by a con­ which there is no general access for acceleration by the large machine siderable amount of shielding made while experiments are in progress. up to 28 GeV. The ring, which has a up of concrete covered with earth. A completely different picture of diameter of approximately 200 m, During operation, the machine is the radiation level around the ma­ houses the vacuum chamber and 100 inaccessible. The same is true of the chine is seen if the high-energy beam magnet units aligned along it. The experimental halls, which are like­ of protons is extracted through the target is located inside the vacuum wise surrounded by shielding built up shielding wall. In this particular case tube and produces scattered protons of concrete blocks. Outside, fences the dose rates become significant or other particles when hit by the are placed on either side of the earth over a rather large area, especially in beam. These particles are collimated ring, making this area inaccessible the beam direction and to both sides through holes in the shielding and led also. of it. After passing through the into the experimental halls to be used During normal machine operation, experimental hall the proton beam for nuclear studies. the radiation level outside the shield- hits a beam trap, essentially a hole made up of massive concrete shield­ ing blocks located in front of a large hill of earth ; but even with the beam passing through air only, dose rates up to 10 mrem/hour have been meas­ ured lately outside the fence in the worst position. This value is approxi­ mately four times the maximum al­ lowable for continuous exposure. For­ tunately this mode of machine oper­ ation has been extremely rare, amounting to not more than a few hours a month. Also it is still possible to reduce the dose rates in such cases, and studies are being undertaken in order to be able to shield off the stray radiation and allow the extract­ ed protons to be used more exten­ sively for experiments under better radiation safety conditions. Fig. 2 shows the general layout of the 28-GeV proton synchrotron (PS), with the injector and the North and Fig. 1. Plan of the CERN 600-MeV synchro-cyclotron accelerator. 1. Vacuum chamber. 2. Target. 3. Magnet. 4. Shielding. 5. Beam South experimental halls. The injec­ channels. 6. Proton experimental hall. 7. Neutron experimental hall.

5 fined to targets, vacuum-chamber wall, magnets or other parts, and places which have been hit by the beam. The concentration depends upon several factors such as beam intensity, exposure time, and half- life of the isotopes formed, and the radiation level will therefore vary from place to place in the accelera­ tor, depending also upon the preced­ ing method and time of machine operation. The safety problems arising from the induced radioactivity in the accelerator parts are of particular concern for all kinds of maintenance and repair work on the machine itself, and also for other work which has to be carried out in nearby Fig. 2. General layout of the regions. CERN 28-GeV proton-synchrotron accelerator. 1. Injector. 2. Ac­ On the synchro-cyclotron, the celerating ring, diameter 200 m. vacuum chamber between the magnet 3. Target area. 4. North hall. 5. poles represents the region with the South hall. 6. East experimental highest radiation level. This is mainly area (in course of construction). due to induced radioactivity in iron. 7. Control rooms. 8. Laboratories. 9. Large-bubble-chamber build­ The level changes from time to time, ing. 10. Hydrogen service build­ but dose rates up to 6 rem/hour have ing. 11. 10-MeV-generator build­ been measured, due to gamma and ing. beta radiation. Strict rules are observed for entering the tank, and written au­ thorization is required. This states the length of time a person can spend ing is barely detectable when meas­ vey measurements are always carried in the tank, judged from dose-rate ured in the plane of the beam. Val­ out before access is permitted. Regu­ measurements and his previous ex­ ues of less than 5°/o of the maximum lations and rules for access are then posure. Special clothes, together with permissible dose rate are generally based on the information obtained. caps and shoe-covers, are used in observed, largely due to neutron Outside the fence and elsewhere on order to avoid contamination, and the radiation. On top of the shielding the site the radiation level is very low dose is monitored by integrating inside the fence, a larger dose rate and not measurable with normal dosimeters. Recently the time allowed exists, going well above the limit of sensitive radiation dosimeters during for work in the tank has been of the 2.5 mrem/hour at spots where there machine operation. order of 10 minutes for each person, are ventilation pipes. This degree of safety has been con­ and for work requiring a longer time As in the case of the synchro­ firmed by special low-level neutron several people share the job. cyclotron there is usually no access measurements carried out in a lab­ Immediately outside the vacuum to the experimental halls when the oratory located 400 m from the chamber a great variation exists in beam holes are open and experiments centre of the PS machine and 110'm the radiation dose rate, ranging from are going on. Several beams are from the SC machine. At this position 100 mrem/hour to nearly 1 rem/hour. usually in operation at the same time an increase in the neutron back­ All work in this region is also limit­ in the South experimental hall, mak­ ground by a factor of 3 was found to ed in time, usually determined from ing this area uncertain from a ra­ be caused by the operation of both the readings of an integrating pocket diation-safety point of view. The pre­ machines together. A similar meas­ dosimeter. diction of radiation hazards due to urement was done at another posi­ beams of particles in the GeV energy tion, 40 m from the SC and approxi­ In the machine hall the dose rate region is difficult, both because the mately 350 m from the PS. This is much less, of the order of 10-15 present knowledge of accurate dose showed an increase by a factor of 5, mrem/hour. measurements is scarce and because which compares favourably with the Since the decay of the isotopes almost nothing is known about the factor of 10 obtained just by going to formed has a great influence on the biological effects which these very an altitude of 3000 m. Assuming a radiation level in the vicinity of the high-energy particles can produce. cosmic-ray neutron level at the CERN machine, it is of interest to know the 2 decay curve. This has been measured When the beam holes are blocked site of 50 n/cm per hour, all these for iron, which is the main material with the accelerator still operating, values are less than l°/o of the maxi­ in the machine. The curve, shown in access is given to the experimental mum permissible radiation level. fig. 3, indicates a rather fast decay to halls. The dose rate measured then The brief indications given here start with, slowing down with time. varies from place to place, and justify the view that the CERN ma­ As a consequence of this, one day's changes also with the beam intensity chines are well shielded and that the cooling time is usually allowed before and according to the target which is site and surroundings can be consi­ major work is done in the tank of being exposed. The dose rate meas­ dered as very safe from a radiation the machine. ured, however, has been found not point of view, when the machines to exceed the maximum permissible work under normal conditions. It should be kept in mind that this level, except in a small region close machine usually operates from Tues­ to the shielding immediately beyond day to Sunday and that repair work Safety during shut-down one of the targets in use. Similar and maintenance are carried out on results have been obtained for the Radiation safety during shut-down Mondays. This means that the per­ North experimental hall when oper­ of the particle accelerators is related missible weekly dose is concentrated ating targets further away from this to the induced radioactivity formed into one day. region. As a general rule, in areas by the beams of high-energy par­ On the proton synchrotron the dis­ where any appreciable amount of ticles produced during operation. This tribution of induced radioactivity radiation is suspected, radiation sur- induced radioactivity is largely con­ extends over a much larger region.

6 Fig. 3. Decay curve for induced radioactivity in iron from the synchro-cyclotron.

As already mentioned, 100 magnet Fig. 5. Decay curve for units are distributed around the ring induced radioactivity in iron from the proton synchrotron. and routine measurements of the radiation level are made for each such section. Fig. 4 shows the dose rate measur­ ed at the different sections at a dis­ samples taken periodically, however, Radioactive waste is composed tance of 10 cm from the vacuum have always shown a very low con­ mainly of parts taken out of the ma­ chamber. It is seen that the rate centration of radioactivity, which chines, and of liquids from the nu­ varies considerably from place to may be explained by the good venti­ clear chemistry laboratory. The solid place around the ring, ranging up to lation systems applied to both ma­ waste offers a greater problem from 2 rem/hour near the targets. chines. Confirmation has been obtain­ the point of view of contamination of Comparing curves taken at dif­ ed from a whole-body measurement radiation detecting devices than as a ferent times, it has been found that of an operator on the synchro-cyclo­ radiation hazard to people. This is the shapes are very similar, but the tron, who showed no sign of radio­ due to the relatively low specific values may well vary from time to active contamination other than radioactivity found in the machine time depending upon how the accel­ caesium-137 and potassium-40, which parts. All parts and materials taken erator has been operating. The values were both also normal and com­ out of the machine areas are inspect­ of dose rate at 1 m from the vacuum parable with the values in people ed and permanent storage of the tube indicate quite clearly that most from Central Europe. larger contaminated metal pieces is of the PS machine ring is quite safe arranged on a concrete floor in the during shut-down, because the Radio-isotopes and radioactive waste open air surrounded by a locked radiation level due to the induced fence. Smaller pieces of metal, and products radioactivity is low. In the target other solid material, are kept in con­ region, however, the level is higher, Radioactive isotopes are frequently tainers in a store used entirely for and precautions are taken when work used at CERN for testing and calibra­ this purpose. is to be done. These precautions con­ tion purposes, and so far more than The liquid waste products are stor­ sist of placing barriers at a safe dose 150 units have been bought by the ed in special tanks which are emp­ limit and of giving time-limited ac­ Organization. Most of these are reac­ tied from time to time as the radio­ cess inside them. The barriers are tor-produced materials in the form activity decays. Before the liquid is moved as the level falls. of encapsulated sources. These are released, samples are measured and a The decay of the induced radio­ kept under control and also inspected dilution is made such as to give a activity in iron which forms the ma­ from time to time. Most of them are concentration of radioactivity lower jor part also of this machine, is kept in two special storage places, by a factor of 10 than the values set shown in fig. 5. Again the short-life although a number of smaller sources forth by ICRP for drinking water. isotopes decay first and give rise to are frequently in use at different This factor of 10 is applied to follow the form of the curve. It is also notic­ laboratories on the site. the Swiss rules. ed that isotopes with relatively long Targets, which have been exposed half-lives are formed, and these will to the beams of the CERN machines Personnel control have the greatest influence on the and are quite radioactive, are fre­ future build-up of the radiation level quently used for nuclear chemistry At present 800 out of 1400 people of the accelerator. studies. This material is handled ac­ working at CERN are occupied with It might also be suspected that the cording to normal procedure and the work involving some radiation ex­ operation of the CERN particle ac­ chemistry carried out in a laboratory posure. These people work either celerators gives rise to radioactive specially designed for radioactive directly with radiation or in areas dust and air contamination. Dust materials. where a radiation dose rate exceed­ ing normal background has been measured. This group of people be­ longs to the category of occupa- tionally exposed personnel and is therefore under continuous radiation control by means of film badges. The film badges are of two kinds, one for gamma radiation and one for fast neutrons. Gamma film badges are carried by all 800, while about 150 are also under neutron-film-badge control. The neutron films are only required for work in areas where a substantial neutron level has been measured ; at the same time, to have access to these areas people are re­ Fig. 4. Typical dose-rate quired to carry neutron films. distribution around the pro­ The gamma films are, with the ex­ ton synchrotron. ception of those for a few groups of people, read every two weeks. Three

7 to four groups, however, among those Fig. 6, Accumulated dose for pre carrying out work on the SC machine ceding 12 months for 5 synchro have a weekly change of gamma cyclotron operators. films. The films are developed and read by l'lnstitut du Radium, in Ge­ neva, which provides CERN with the results. The film badges for fast neutrons are changed only once a month, as the fast-neutron exposure at CERN occurs usually at a rather low dose rate. These films are developed and read at CERN. The information obtained from the film-badge readings gives an idea of the safety of CERN personnel against radiation. It should be looked upon in relation to the ICRP maximum permissible radiation exposure, which WHO'S WHO IN CERN is 5 rem per year, not exceeding 3 rem for 13 consecutive weeks, and the results for 1960 are quite low : 0 - 1 rem 703 people 1 - 2 rem 72 people Johan BAARLI Head of Health Physics 2 - 3 rem 11 people 3 - 4 rem 4 people 4 - 5 rem 2 people Argonne Cancer Research Hospital, at the > 5 rem 1 person same University, where he worked with In 1961 there seems to have been Prof. Skaggs. a somewhat increased exposure, espe­ About this time Norsk Hydro's Institute cially of those groups carrying out for Cancer Research was created as part maintenance work and repair of the of the Norwegian Radium Hospital, and SC accelerator. This fact can be seen in the autumn of 1953 Dr. Baarli was from fig. 6, where the accumulated asked to return to his native country to dose for the preceding 12 months is plotted as a function of time for the take charge of its Department of Bio­ five most exposed people at present physics. When he arrived, there was just working on this machine. It is clearly an empty building. Now, the departments seen that a change of exposure oc­ of biophysics — still the only one in curred around April/May, which can Scandinavia —, biochemistry, and radio- be explained by an improvement in biology, together employ some 60 people, the SC beam intensity. As a result of of whom 20 are qualified scientists. The this, steps have been taken in order hospital itself has 310 beds, and its to distribute the work, and conse­ equipment includes a 31-MeV betatron quently also the radiation exposure, over more people. together with more conventional x-ray equipment. In addition there are clinical Together with the personal monitor­ Johan Baarli, who arrived at CERN at irradiation sources utilizing radiocae- ing of people for radiation exposure, the beginning of April, 1961, to take sium, designed by Dr. Baarli and de­ there is a periodic medical check. charge of Health Physics, was bora in scribed by him in a paper to the Con­ This consists of blood and eye exami­ Norway on 23rd June, 1921. His birth­ nations, the eye examination being of ference on the Peaceful Uses of Atomic place, Eidsvoll, some 60 km North of special importance for cateract for­ Energy in Geneva in 1958. Among the Oslo, is of interest as the place where the mation which is of concern in con­ other things he did whilst at the Institute nexion with neutron exposure. The constitution of Norway was drawn up were the development of new instruments frequency of the medical inspection in 1814. for dosimetry ; the study of radiation is determined by the radiation expo­ effects on biological material, including sure, and takes place at least once a Upon leaving school he entered the the development of a light-scattering year. University of Oslo as a student in the device and viscometer for studying radia­ From what has been said, it can be Faculty of Sciences, but his studies were tion effects on large molecules ; and the concluded that the CERN site repre­ interrupted when the occupation forces sents an area with a low radiation closed the University in 1943. development of new instruments for low- level, considering the location of very level counting of radiation used in studies It was not until 1950 that he was able high-energy accelerators. This is pri­ of metabolism. to conclude his studies with bis thesis marily due to the well-designed shielding arrangements applied to on 'The construction of a neutron Dr. Baarli is still a member of the these machines. On the other hand, generator and the study of neutrons Scientific Advisory Council of Norsk it should not be forgotten that our from d-d reactions'. He then became a Hydro's Institute for Cancer Research. knowledge about the dosimetry, and teacher at the University of Oslo. He is also Secretary of the Nuclear Re­ also the radiobiology, of the great search Committee of the Royal Norwegian variety of particles produced espe­ In 1952 he left Norway and went to Council for Scientific and Industrial cially by the PS machine is scarce, work with Prof. Zirkle at the Institute Research, Member of the Joint Committee and represents a field of studies of Radiobiology and Biophysics of the on Scientific Institutes in Norway, Secre­ CERN is very interested in. In conse­ tary to the Committee on Atomic Energy quence, research problems in high- University of Chicago, as a postdoctorate energy dosimetry form an additional fellow financed by the Norwegian Can­ in Technological Studies, and past Vice- part of the radiation-safety activity cer Society and the U.S. Atomic Energy President of the Norwegian Physical at CERN. Commission. Later he moved to the Society.

8 From 5 to 9 June 1961, a rather unusual conference was held at CERN. This was the 1961 International 'Two features appear highly desirable in future Conference on Theoretical Aspects of Very High Energy experimental work : great flexibility and good Phenomena, sponsored by the International Union of Pure and Applied Physics, which brought together intensity. For many problems, one wants to go to with their CERN colleagues some 50 other physicists high energies ... but one gets the impression that from over a dozen other countries. The discussions were energy increase should not go at the cost of the mainly on theoretical subjects, but their aims were flexibility and intensity requirements. We have strictly practical — namely to try to determine which encountered only very few arguments to go to kinds of accelerating machines would be most useful extremely high energies... in about 10 years' time. It is already obvious that the 'We should stress, however, that such consider­ results from the present high-energy machines are only ations are bound to be extremely conservative, steps on the way to our fuller understanding of matter, since they are based on questions and problems and it is necessary to plan now the accelerators that will be needed to carry the results further in the 1970s. suggested in the most immediate way by our 'Very high energy', with reference to a system of present state of knowledge and since they do not nuclear reactions, is not easy to define. As Prof. Van take into account the well-known and drastic Hove pointed out in his concluding lecture at the Con­ limitations of our power of imagination... As is ference, its appropriate lower limit depends very much often the case, unpredictable features may turn on the processes being considered ; in general it lies out to overshadow all present speculations and between 100 MeV and 1 GeV for weak and electro­ conjectures and open up an entirely new chapter magnetic interactions, and at a few GeV (centre-of- of high-energy physics.' mass energy) for strong interaction processes. Above these energies, the range extends into regions attainable From the concluding lecture given by L.Van Hove. at present only by cosmic rays, which involve energies sometimes of tens of thousands of GeV. * The task of the theoreticians is to describe nuclear processes in mathematical terms. Their equations, evolv­ one form of the theory is also a possibility, as well as ed to explain current experimental results, suggest the quantitative study of weak lepton-nucleon coupling new experiments, which must be carried out to provide by means of the reactions between neutrinos and verification. The purpose of the CERN Conference was protons or neutrons. to review the latest theories in relation to the experi­ The cross-sections for all these reactions are very mental results obtained with the largest present-day small, however (of the order 10~37 to 10~41 cm2), and a accelerators and with cosmic rays, and to suggest the high neutrino flux is vital. most interesting experiments that could be used to test these theories. Strong interactions Nuclear processes fall into three separate classes according to their probability of occurence. Thus we So far, the use of the larger machines to study strong distinguish strong, electromagnetic, and weak inter­ interactions (those charcterized by collisions of nucleons actions, and at the present time describe them by three and pions) has not revealed much that is remarkable. If different kinds of theory. one considers the most common, or 'dominant' processes, the experimental results can be understood on the basis of naive, simple considerations to within 5 or 10%. Weak interactions Attempts to understand the more detailed features, Weak interactions are characterized by the beta- however, lead to considerable difficulty, and it becomes decay of radioactive nuclei, the decay of pions and interesting to know whether the deviations from simple muons, and the interactions of neutrinos with matter. theory get worse at higher energies, or whether they The latter processes are of the greatest theoretical disappear. Recent results obtained at CERN were pre­ interest, particularly as the present 25-30 GeV acceler­ sented in papers by G. Cocconi, K. Winter, and D.R.O. ators can just provide sufficient neutrinos to make Morrison, while R. Hagedorn showed how these and their study feasible. Papers from CERN contributing to other results were only partially described by the the discussion of weak-interaction theory were read simplest theories of particle production in high-energy by S.M. Berman and by J. Nilsson and R.E. Marshak. collisions. The most interesting speculations, qualitatively, are on Various new 'models' have been proposed in attempts the existence of two distinct kinds of neutrino, and of a to arrive at a better understanding of the experimental new particle (a boson with mass of the order of the facts, and the 'one-pion-exchange model' was discussed nucleon mass or higher). by F. and G. Salzman (University of Colorado) and by G. Bernardini reported on progress with the CERN F. Selleri and E. Ferrari. This theory refers to the experiment on the first of these. A search for the phenomenon of multiple pion production, or 'pioniz- existence of self-interaction terms which arise in ation' as it was called by Cocconi. To explain the pronounced diffraction effects that occur in small-angle scattering of strongly interacting particles, the 'strip approximation in the Mandelstam representation' has * On two occasions since May 1960, interactions involving at least lOio GeV have been observed in New Mexico. (Continued on p. 15)

9 brought together in equal numbers members of the 'pre-war' and of the 'post-war' eras of physics. The list is so short it is worth quoting in full : 50th Anniversary of the Bethe, N. Bohr, Gorter, Heisenberg, Heitler, O. Klein, Moller, Oppenhei- mer, F. Perrin, Rosenfeld, Wigner, and Yukawa, representing the gener­ ation that grew up with modern quantum mechanics ; Chew, Dyson, Solvay Physics Meeting Feynman, Gell Mann, Goldberger, Kaller, Mandelstam, Pais, Salam, Schwinger, Tomonaga, and Van Hove, leader of the theoretical physics divi­ sion of CERN, representing the later generation that has developed mod­ Most scientific conferences nowa­ result of a meeting with Nernst the ern field theory since 1947. days seem to involve too many peo­ first of the 'Conseils de Physique ple; too many papers prepared in ad­ Solvay' was arranged in the following The theme was set by the prepared vance and read at great speed ; and year, from 30 October to 3 November papers: Feynman on electrodynamics, too little time for thought. The 12th in Brussels. Heitler also on electrodynamics, pro­ Solvay Physics Meeting, held at the Solvay's idea was to gather together viding an interesting comparison; Free University of Brussels from 9 for one week a score or so of the Goldberger and Mandelstam on dis­ to 13 October, 1961, was an exception. leading scholars in some scientific persion relations — an old concept Like its predecessors, this meeting, field, and to give them the facilities recently applied in a new field ; Pais held to mark the 50th anniversary of for exchanging ideas without inter­ on the development of the theory of their foundation, had few partici­ ruption. That idea is still followed weak interactions in the five years pants, few formal papers, and plenty today. The members who attended since the discovery of the non-con­ of time for informal discussion. the recent meeting, to discuss the servation of parity ; and so on. As Ernest Solvay, who had made a 'Quantum theory of fields', had the discussion developed, however, ideas very considerable fortune out of his rather rare opportunity of being focussed on the concept of 'element­ invention of a new process for manu­ able to discuss among themselves not ary' particles. Just how can one facturing soda, had a great interest so much the latest theories but the decide whether a particle is element­ in the advancement of learning and whole recent development of this ary or composite, when the number devoted a large part of his money subject, thereby helping to put these of new particles seems to be con­ to the foundation in his native Bel­ theories in better perspective. Pre­ tinually increasing, and structures gium of research institutions in the pared papers were few, and in any are found for the old established natural and social sciences. In 1910, case of a general survey nature, and ones ? How can a mathematical for­ his desire to establish International most time was spent just on the ex­ mulation be arrived at that will Institutes of Physics and Chemistry change of ideas. enable us to define these particles brought him into contact with var­ This fiftieth anniversary conference precisely ? Possible criteria were ad­ ious scientists of the day, and as a was especially interesting in that it vanced and discussed. Possible exper-

They worked at CERN

As is only to be expected of a unique laboratory serving a dozen European

nations, the staff of CERN is not static. Many new scientists and engineers wish to

come to take advantage of its special facilities ; but eventually most of them will go again, back to their own countries or perhaps further afield to gain even more

experience. We could perhaps tell readers who the new members are, where they

have come from, and what they have been doing, but it seems preferable instead

to mention those who have left, what they have done at CERN, and how they will

use this experience in future. Unfortunately we cannot mention everybody, and

our selection is only a little better than random, but in the following paragraphs

we have noted some of the those of whom we now have to say 'they worked at

CERN\ J. Leroux presenting J. B. Adams with a photo album autographed by all PS staff members (27 July 1961).

John B. ADAMS left the Organization His reputation, however, is linked a ceremony was held on the steps of the on 1 August to become director of the with that of the proton synchroton. As Administration Building. Speeches were Culham plasma physics laboratory of the director of the PS Division from 15 No­ made by Mr. Leroux and Prof. Bernar- U. K. Atomic Energy Authority. He was vember 1953, he provided the knowledge, dini. In the course of his reply, Dr. originally to have left a year earlier, but drive, and enthusiasm, to enable this Adams expressed the hope that he could following the death of Prof. Bakker in machine, the first of its size in the world, still help in the work of the CERN labo­ April 1960, his stay was prolonged by to function so successfully immediately ratory ; he has already attended a his appointment as Director-General of after its completion. meeting of the Scientific Policy Commit, CERN. To mark the occasion of his departure tee in November.

10 iments were planned which might throw more light on the problem. Of the types of experiment propos­ ed, it is perhaps interesting to note that two of the most important ones are both being considered at CERN. In one case the energy dependence of the results of 'peripheral' colli­ sions (which are thought to involve the transfer of a fundamental par­ ticle) can give information on the particle exchanged. In the other, elas­ tic collisions between particles, with very high momentum transfer, will provide valuable information on the scattered particle. The outcome of the Solvay meeting itself gives no special cause for ex­ citement, though as Lorentz said in his presidential address to the first one, it is not possible to tell in ad­ vance whether great ideas will come out of such a meeting or whether they will perhaps come to some person alone, completely independ­ ently. Such an interchange of ideas cannot fail to have its effect, how­ ever, and the Solvay Physics Meet­ ings have certainly marked the way taken by atomic and nuclear physics Participants of the 1st Solvay Physics Meeting in 1911. Seated, from left to right: Nernst, Brillouin, Solvay, Lorentz, Warburg, Perrin, Wien, Mme Curie, Poincare. Standing: Goldschmidt, Planck, in the last fifty years. At the first, Rubens, Sommerfeld, Lindemann, De Brogiie, Knudsen, Hasenohrl, Hostelet, Herzen, Jeans, Planck's quantum law was discussed. Rutherford, Kamerlingh Onnes, Einstein, Langevin. At the fifth, in 1927, on 'Electrons and photons' the topic was the new quantum mechanics. At the seventh, known to exist, it is interesting to have shown themselves more and in 1933 (the last before 1948) the recall some of Lorentz's words at that more incapable of piercing the dark­ subject was 'The structure and pro­ first meeting : ness that is closing in all around.' perties of atomic nuclei'. 'We are far from the complete He could go on to hail Planck's Looking back on fifty years, and spiritual satisfaction that (we had) quantum hypothesis as 'a precious considering how puzzled theoretical ten to twenty years ago. Instead, we ray of light'. We, it seems, will have physicists are today by the multitude now have the feeling of being up to wait a little longer for eqUivaient of experimental phenomena now against a barrier ; the old theories illumination.

Andre DECAE left CERN on 31 subsequent checking after excitation. An since July 1955, his first year being spent March to take up an appointment as idea of their achievement here can be at the Carnegie Institute of Technology Scientific Secretary in the Conseil Inter­ gained from the knowledge that the in Pittsburgh to gain experience with national des Unions scientifiques at The circle formed by the magnets was made their 430-MeV synchro-cyclotron. Coming Hague. This Council acts as a co-ordi­ true and level to within a few tenths of back to Geneva, he was concerned with nating and advisory body for the inter­ a millimetre over its whole diameter of the putting into operation of the SC national scientific unions and Mr. Decae 200 m. This vital contribution to the machine, particularly in the development is responsible for all matters concerning construction of the accelerator was proved of the Penning ion source. Following the geodesy and geophysics. His office is by the circulation of the first beam in successful operation of the machine for moving to Rome in January 1962. September 1959. nuclear-physics experiments, he turned He and Jean Gervaise came to Geneva Mr. Decae was President of the Staff to the production of polarized protons, in December 1954 from the Institut Geo- Association in 1960. and his method has been applied success­ graphique National, in Paris, and began fully at 4,5-MeV on the small cyclotron. by conducting stability studies on the At the same time, he developed inde­ moraine before any buildings were begun. Pierre GUILLOT left CERN on 31 pendently the idea of stochastic acceler­ This work, which involved careful meas­ March 1961 for the Euratom nuclear ation for synchro-cyclotrons, and one of urements lasting about a year, with research centre at Ispra, in Italy. There his two proposed methods for increasing accuracies of 0,1 mm, showed that the he will supervise the nuclear security the beam intensity in this way has been moraine was not sufficiently stable and system, thus occupying a similar post to tried out with success on the SC in 1961. that the PS machine foundations would that which he filled at CERN. Coming to Dr. Keller has gone to Lausanne, where have to be sunk to the underlying mo- Meyrin in January 1959, he was involved he is working with E. Weibel at the lasse rock. A further year's work, in principally in the dosimetry of fast neu­ newly formed plasma physics research collaboration with the seismographic trons and in the spectrometry of stray centre supported by the Fonds National station at Neuchatel, showed that the radiation. Suisse de la Recherche Scientifique. mo lasse was subject to seismic vibration, Dr. Guillot was born in 1930 at Hanoi, and this led to the adoption of elastic in Indochina, and studied principally in supports for the foundation ring, designed Paris at l'Ecole superieure de Chimie et Alf OSTLUND left CERN on 31 July to insulate the machine from such disturb­ de Physique. He obtained his doctorat es to become technical director of a new ances. sciences in Paris, at Flnstitut Pasteur. nuclear electronics firm in Geneva. Six During the construction of the proton years previously he had come from the synchrotron Andre Decae and his team University of Uppsula, where he had played a major part in the initial posi­ Robert KELLER, who left on 30 April, worked for 5 years on their 180-MeV tioning of the magnets, and in their had been a member of the CERN staff cyclotron. At CERN he spent some time

11 products from the action of high-energy protons on iron. Last year at CERN (cont.) Many of the experiments using the synchro-cyclotron concerned muons. Further measurements on (g-2), the anomalous magnetic moment of the muon, were carried out that the Trieste team returned home at the end of their to reduce the experimental error to ± 0,5 % and the final experiment on charge-exchange scattering of negative pions result was awaited at the end of the year. In another in hydrogen ; after this, in August, came a new visiting team experiment, about 380 000 bubble-chamber pictures were from Argonne National Laboratory, U.S.A., led by Prof. A. obtained of muons stopping in highly purified hydrogen. Roberts. Five thousand tons of shielding had to be placed X-rays emitted when muons are captured into 'atomic' in position when the neutrino experiment attempted to find orbits have also been studied for two ranges of nuclear whether the neutrino emitted in the decay of a pion is the mass, to obtain information on nuclear radii. same as that involved in nuclear beta decay. The new CERN heavy-liquid bubble chamber was used for this during May- Apart from carrying out measurements on tens of July, together with the Ecole Polytechnique (Paris) chamber, thousands of track-chamber photographs already taken, the using a mulfiplate cloud chamber and large-area scintillation Data Handling Division actively pursued the development of and Cerenkov counters for background measurements. Un­ more automatic machines that would be able to handle fortunately, the number of neutrinos, which are extremely greater numbers in future. The 'Mark O' version of the lep Y or Hough-Powell flying-spot apparatus, was tested in non-reactive particles, proved to be much lower than r originally expected, and insufficient to allow any results to May by a team composed of personnel from Brookhaven be obtained. Only seven possible events were found among and Berkeley, in the U.S.A., and the Rutherford Laboratory the 150 000 pictures taken, and revised estimates of the in England, as well as CERN. Further tests were carried out number of neutrinos available indicated that only 1 event in June, and construction of the 'Mark I' working version in 100 days was to be expected. The experiment will be was at an advanced stage at the end of the year. Design continued, using a 'magnetic horn' to increase neutrino studies by the Accelerator Research Division have continued intensity, and a bigger detector, a multi-ton spark chamber. on the two proton storage rings, proposed for the CERN Another search for something rare, or non-existent, proton synchrotron to give two colliding beams of particles. resulted in the establishment of lower limits of between This would enable, for instance, proton-proton collisions to 10"35 and 10"39 cm2 per nucleon for the production cross- be investigated in the region of 50 GeV centre-of-mass section of magnetic monopoles. energy. Construction of the electron beam-stacking model Many experiments on the PS utilized proton or pion has suffered some setbacks because of delayed deliveries, beams to carry out measurements of a number of different but the RF system is ready and much progress has been reaction cross-sections for these particles. Important studies made with the all-important ultra-high vacuum. were carried out on the quasi-elastic small-angle scattering Some controversy exists over the relative value of collid­ of protons on protons. The absorption cross-section for 10 ing beams, and the Division has also made a start on the and 13,5 GeV photons was measured for a number of study of an alternative suggestion of building a new elements. An experiment of interest in connexion with synchrotron giving much greater energy. Accelerated cosmic-ray-induced activities in iron meteorites was the protons of over 1000 GeV would be needed, however, to measurement of cross-sections for a number of spallation give the same centre-of-mass energy for the proton-proton

working on the construction of a magnet for other accelerators. During his stay at ponsible for the preparation of the Safety regulator for the synchro-cyclotron and CERN he was also at some time a mem­ Codes now in use. was then responsible for the formation ber of the Leading Board and of the Like many British engineers, Mr. Webb of an electronics maintenance section. library committee. received his early training as an appren­ This was originally for the SC machine, At Heidelberg, where he occupies the tice in an industrial works, studying part- but it is now concerned with the repair, chair of applied physics at the Max time at a Technical College as an external checking, and calibration of electronics Planck Institute, Prof. Schmelzer is still student of London University. Subse­ instruments used throughout CERN. concerned with accelerator development. quently he became an Associate Member He is a consultant to CERN, and also both of the Institution of Civil Engineers chairman of the Wissenschaftlicher Rat and the Institution of Mechanical Engineers, (scientific council) which advises on the and in the course of a varied career first Christoph C. SCHMELZER, one of 6-GeV DESY (Deutsches Elektronen- in industry and then in Government serv­ the earliest CERN staff members, Left on Synchrotron) accelerator at Hamburg. ice was one of the original design 22 March to return to Heidelberg Uni­ engineers for the Atomic Energy Re­ versity, where he began studies on the search Establishment at Harwell. acceleration system of the future Euro­ pean synchrotron as far back as the end Frederick A. R. WEBB returned to of 1952. This followed his work under England at the end of December after On 15 August, Dr. Toyio YAMAGUCHI Prof. Bothe, when he made a study of being at CERN since 1 October 1956. left CERN for his home country, where phase stability in microtrons and played Originally released for a period of two he has been appointed to the Chair of an important part in the redesign of the years from the Ministry of Works in the Physics at the University of Tokyo. Heidelberg cyclotron. United Kingdom, he has stayed to see Born on 29 January, 1930, Dr. Yama- After coming to Geneva in 1954, he the putting into operation of the 28-GeV guchi received his education in Japan, became responsible for the design, devel­ PS accelerator, and the beginning of fur­ where he was a student of Prof. Toga- opment, construction and final testing ther expansion on the site. As Site En­ naka. He obtained his Doctorate in Phys­ of the PS acceleration system, and was gineer, and later Deputy Leader of the ics, with a thesis on the 'Theory of also deputy to the Division Director. The Site and Buildings Division, he has been mesons'. results of his work were seen on 24 No­ responsible for all the civil, mechanical, Dr. Yamaguchi had been at CERN vember, 1959, when the first beam was and electrical engineering installations since 1957, with a Fellowship from the accelerated to full energy so soon after and maintenance, and for the overall Ford Foundation. As a member of the completion of the machine construction. control of transport, security and fire Theoretical Physics Division he carried He then continued with studies of radio- services. As chairman of the organi­ out a number of studies, mainly on the frequency systems both for the PS and zation's Safety Committee he was res­ subject of weak interactions.

12 experiments. The Theory Division arranged an International Conference in the summer (as reported on p. 9) to clarify 19th Session of CERN ideas on the most useful types of machine to aim at, from the point of view of the physicists. Council

The total number of people working af CERNr including Mr. Jean Willems (Belgium), fellows, supernumeraries, and visitors, was 1459 in mid presided over the 191 h meeting of November. Visitors coming from 33 countries worked at the Council, held at CERN on the CERN last year. 2 June 1961, at which the following delegates and advisers took part: In 1961, the laboratories used about : Austria: 35 500 000 kWh of electricity, Prof. W. Thirring

3 3 438 000 m of cooling water, f Prof. F. Regler

res Mr. E. M. Schmid JJLSSS. ''* liquid hydrogen, Mr. H. Vavrik 370 000 litres liquid nitrogen. Belgium: 7,3 km of cable trays have been laid in the PS East Prof. J. Serpe Prof. J. Franeau experimental area. Mr. M. Freson In the six months from May to November the Scientific Denmark: Information Service produced 1,8 million pages of offset. Prof. J. K. Boggild The Engineering workshop worked 17 070 man hours, and Mr. O. Obling Federal Republic of Germany: the SB Main workshop 50 498 man hours. Prof. W. Heisenberg The Mail Office handled 31 000 letters per month and Dr. A. Hocker distributed internally 70 000 items per month. Prof. W. Jentschke 576 visitors per month were shown over the Organization Prof. W. Paul France: by the Public Information Office alone. Mr. F. de Rose The total floor area in offices and laboratories is now Prof. F. Perrin 65 000 m2. M. F. Neumann Mr. J. Courtillet Greece: Mr. A. Vlachos Prof. A. Embiricos This last year, the CERN staff was grieved Prof. Th. Kouyoumzelis to loose three of its members: Prof. Th. Kanellopoulos Mr. S. Boukis Gilbert LAILLY, from the Site and Buildings Italy: Division, killed in an accident on 4 March 1961; Mr. G. B. Toffolo Andre TOURNIER-COLETTA, from the Accel­ Prof. E. Amaldi erator Research Division, who died on 1 Dr. C. C. Bertoni August after a long illness ; Mr. M. Sabelli Leon FLATOT, from the Data Handling Di­ Netherlands: vision, who was killed with his wife in a car Mr. J. H. Bannier accident on 3 November. Prof. S. A. Wouthuysen During the same period, on 17 May, Paul Mr. C. E. I. M. Hoogeweegen CHARRIER, working for a Parisian contractor Prof. H. J. Groenewold on the site of the Organization, was killed as Norway: a result of a fall. Prof. H. Wergeland Mr. M. Huslid CERN COURIER extends to their families Spain: the deepest sympathy of those who, in one way Prof. J. Ofero-Navascues or another, had the privilege to be their Mr. J. M. Aniel-Quiroga Mr. P. Temboury friends or colleagues. Miss A. Vigon Mr. R. Ortiz Sweden: Dr. G. Funke Prof. I. Waller Switzerland: Prof. P. Scherrer Mr. A. de Senarclens Mr. R. Bieri United Kingdom: Sir Harry Melville Sir John Cockcroft Mr. S. H. Smith Prof. C. F. Powell Mr. G. Hubbard Mr. R. G. Elkingfon Yugoslavia: Prof. E. Supek Mr. B. Komatina

Mr. F. Alacam (Turkey), observer, and Mr. A. Baumann, from the Swiss Finance Audit, also attended. Among items on the agenda consider­ ed by the representatives of the 14 Member States were : — the progress reports of the Director- General and the Heads of Divisions, — the admission of Turkey as an observer to the Council, — the long-term scientific policy, — the election of a new member to the Scientific Advisory Committee (Prof. W. Genfner taking the place of Prof. W. Heisenberg). A plaque to the memory of Prof. C. J. Many new features added to the CERN site in 1961 appear in this picture, mainly the East Bakker was inaugurated in the lobby experimental area of the PS (centre). bordering the Council Room.

13 Nuclear Emulsion work at CERN by J. COMBE and W.O. LOCK, Secretaries of the Emulsion Experiments Committee

The Group at CERN using the nuclear emulsion tech­ This introduction to one of the three experimental tech­ nique has, by its intrinsic nature, and by the functions niques used at CERN (nuclear emulsions, electronic counters of CERN, a triple task to fulfil : and track chambers) will be followed by other texts on the most important technical aspects of the 'Emulsion' work. a) To make use of the two CERN accelerators to carry out research in high energy nuclear physics using the emulsion technique. Some experiments may be carried out in collaboration with groups from mem­ Some of the experiments carried out in collaboration ber and other States. with outside groups (between parenthesis) are : b) Being involved in the general activity of CERN, it a) Study of the processes by which a high energy pi- must always be ready to help other research groups, meson produces two other pi-mesons with a small who from time to time, may have occasion to use the energy transfer to the nucleus (Bari, Bristol, CERN, emulsion technique. Lahore, Milan). At the same time studies have been c) To give all possible help to outside 'Emulsion Groups' made of the production of electron pairs by pi- to carry out the experiments they propose and carry mesons. out independently. b) Search for magnetic monopoles (Berkeley, CERN, Rome). All proposals for experiments from either the CERN Group or outside groups, are received by the Secretaries c) Measurement of the lambda-zero magnetic moment of the Emulsion Experiments Committee. The Commit­ (CERN, Lausanne collaboration for the test run, tee considers the scientific value of each experiment which will be carried out at the PS in January 1962, before submitting it to the Nuclear Physics Research using a pulsed magnet-coil). Committee. After a proposal has been accepted by the d) Study of antiproton-proton elastic scattering in the two Committees, the CERN Group considers how best energy region of 10-50 MeV (CERN-Lahore collabo­ the proposed experiment can be carried out in relation ration). to the general programme of the two accelerators, and e) Exposure of emulsion stacks, principally to proton to its own programme. If all the practical conditions are and pion beams, for many laboratories : last year for satisfied, there are two ways of carrying out an experi­ 26 laboratories in member States and 11 in other ment through the CERN Group: countries.

1) A collaboration may be set up between the CERN 2) All the responsibility, with respect to CERN, for an Group and one or more outside Groups, arising from experiment and its realization is taken by the outside a common agreement between the teams on the group which proposed the experiment. A physicist lines of research that they wish to follow. One or of the CERN Group acts then as a linkman between more of the physicists of the CERN Group take part the outside group, the Divisions responsible for the in the experiment and assume complete responsibility two accelerators, and the Emulsion Group, who of for it with respect to the CERN authorities. In fact, necessity are involved in the execution of any all the experiments undertaken by the CERN Group experiment. This physicist will try to assist in solv­ have been carried out in this type of collaboration. ing the technical problems which arise. In general The Group has developed alone two techniques this scientific and administrative aid can be consid­ which are available for the use of outside groups : ered as part of the general facilities which CERN the pulsed magnet equipment (which can yield fields makes available to its member States and, in a of 200 000 gauss) and the extensive facilities for the certain measure, to non-member States. processing of nuclear emulsions. The following experiments fall in this category : a) The experiment proposed by Prof. B. Peters of Copenhagen on the production of hyperons and the study of their properties. b) Study of different reactions produced by 1,5 GEV/c separated negative K-mesons in nuclear emulsions. This experiment, foreseen for Spring 1962, is entirely under the responsibility of about twelve outside laboratories. c) Studies of fission phenomena induced by pi-mesons and protons in heavy elements, such as uranium, thorium and bismuth (Rome, Naples). The CERN emulsion group is also engaged, from time to time, with problems which are principally of interest to other groups in CERN, for instance : a) for the neutrino experiment, in July 1961, the emul­ sion technique was used to determine the energy and intensity distributions of the pi-mesons coming from a PS target; b) measurements have been made on the attenuation of protons in concrete shielding blocks. The results are of interest to CERN, and to those laboratories which are constructing large accelerators (Harwell, Ham­ burg, Stanford, etc.) ; c) measurements have been made also of the radiation The 200 000 gauss pulsed magnet (right) was used by the CERN Nuclear pattern at the junction of the PS ring with the new Emulsion Group in 1961. East experimental area.

14 VOTRE MAISON DE CONFIANCE POUR Microfilms — Appareils phofographiques et disposififs de lecture - Locations de came­ ras - Travaux de developpement en regie. Photocopies — Appareils d'eclairage et dis­ posif ifs de developpement - Papiers pour photographies - Installations pour la photo- copie. Heliographie — Appareils d'eclairage et ma­ chines a developper - Nouveaute : HELIO- MATIC, machine a heliographier avec VARI- LUX permettant de faire varier la puissance d'eclairage - Papiers pour developpements a sec et semi-humides. Bureau-Offset — Machines et feuilles d'im- pression presensibilisees avec I'OZASOL. Dessins — Machines a dessiner JENNY et combinaison de dessins - Papiers a dessin (papiers pour dessins de details), lisfes de pieces, papiers fransparents (a calquer), papiers pour croquis. Meubles pour serrer les plans — « Systeme a suspension, a soulevement et a abaisse- ment». Installations de reproduction pour helio- graphies, impression de plans, photocopies, travaux de photographie technique, reduc­ tions, agrandissements, travaux de deve­ loppement de microfilms.

- OZALID ZURICH Seefeldstrasse 94 - Telephone (051) 24 47 57

CERN Theoretical Conference (cont.) been devised, with considerable success, and this was described by D. Amati and S. Fubini. As well as the dominant processes there are also less- frequent 'exceptional' processes that are still due to strong interactions. Among these, an interesting class at present being studied is that of 'peripheral collisions' these being inelastic collisions involving a relatively small transfer of momentum and energy. Current exper­ imental results can be partially explained by either the one-pion-exchange model or by 'diffraction dissociation'. This was discussed by B.T. Feld. More experiments in other energy ranges are necessary to test those theories further.

Electromagnetic interactions Agreement between theory and experiment is very much better in the study of electromagnetic inter­ actions, and the main interest is in trying to extend the limits within which the theory can be said to be cor­ rect. Progress on the preparation of electron-scattering experiments with colliding beams was reported from Stanford (U.S.A.) and from Rome.

Conclusions Apart from those mentioned above, further contribu­ tions from CERN were given in papers by T. Ericson, F. Cerulus, and J.D. Dowell, B. Leontic, A. Lundby, R. Meunier, G. Petmezas, J.P. Stroot and M. Szeptycka. A. Schoch reported on the possible future facilities for producing the phenomena of interest to the physicists. Although no clear-cut decision on a future accelera­ tor, could be arrived at, ideas were clarified and the main lines of approach seen more clearly, as shown by the extract we have given of L. Van Hove's concluding lecture.

15 SIEMENS A versatile range INSTRUMENTATION of manufacture

Measurement and control in thermal and processing techniques

Electrical metrology

Electronic microscopy

Non-destructive testing of materials

Measurement, of mechanical quantities

SIEMENS & HALSKE AG Berlin • Munchen Sale Agents for Switzerland SIEMENS E L E KT R I Z I TATS E R Z E U G N I S S E AG Zurich • Bern • Lausanne NIELS BOHR

Hommage par le Prof. V.F. Weisskopf, Direcfeur general, prononce devant le personnel de 1'Organisafion Euro- peenne pour la Recherche Nucleaire (CERN), le 23 novembre 1962.

Chers Amis et Collaborateurs,

Nous sommes reunis eet apres-midi pour rendre hom­ mage a Niels Bohr. Niels Bohr est pour nous le symbole, la source et l'architecte principal de nos travaux. C'est grace a lui, par lui et avec lui que les bases sur les- quelles reposent nos travaux et notre existence ont ete creees. C'etait un grand homme. Comment definir la grandeur? Celui qui ouvre de nouvelles voies et qui cree une nouvelle fa con de penser peut etre qualifie de grand homme; en verite, Niels Bohr, par sa personne et par sa vie, repond a cette-definition. .L'influence -de ses travaux est ressentie dans chaque aspect de notre vie. La science moderne a transformer notre monde. Elle est devenue le f acteur predominant de notre pensee, de notre culture, de la politique meme, et elle commande l'orien- tation de l'humanite pour les prochaines decades. Nous ne pouvons pas encore evaluer la signification reelle du developpement engendre par les travaux de Niels Bohr. Nous sommes trop proches de sa vie. On ne rea­ lise que de loin combien le Mont-Blanc domine les autres montagnes des Alpes.

C'est en 1885 que naquit Niels Bohr. Sa carriere de savant debuta en 1905 environ et continua jusqu'a sa mort. Quelle epoque pour un physicien ! II commenca ses travaux alors qu'on ne connaissait rien de la struc­ ture de l'atome et les termina lorsque la physique atomique, creee par lui, avait atteint sa maturite. En 1905, la science, et notamment la physique, n'etaient pas ce qu'elles sont a l'heure actuelle. Examinons com­ ment se presentait la physique a cette epoque.

C'etait une epoque interessante. C'etait 1'annee ou Einstein enoncait son concept de la relativite speciale et ou une multitude de phenomenes nouveaux etaient decouverts, mais non expliques. C'etait l'epoque, quel- ques annees plus tard seulement — de la grande decou- verte du quantum d'action par Planck. Rares etaient ceux qui avaient remarque le nouveau document de Planck et encore plus rares ceux qui en avaient saisi la signification. C'etait une epoque ou les domaines de la chimie et de la physique etaient eloignes l'un de 1'autre. La chimie, d'une part, representait la science de la ma tier e et de ses proprietes specifiques. L'atome etait un concept de chimie — les atomes de l'or, de l'oxygene, de l'argent, constituaient autant d'entites specifiques dont l'existence etait admise sans etre comprise. La garde dans ses documents et a des reunions que cela ne physique, d'autre part, etait une science de proprietes pouvait etre l'explication finale, que la decouverte d'un generates, du mouvement, du rapport de la tension a la principe fondamental s'imposait d'abord pour com- deformation, des champs electriques et magnetiques. prendre reellement le processus de la quantification de Les deux disciplines etaient tres eloignees. On ne pou- 1'atome. vait pas encore repondre a la question : « Quelle est la source des proprietes de la matiere ? ». Bohr eut la grande chance de se trouver au debut, peut-etre de- Nous abordons maintenant la deuxieme periode de vrions-nous dire plutot que Phumanite eut la grande ses travaux; les annees 1923 a 1932. Ce fut la grande chance qu'il fut la a ce moment crucial. periode pendant laquelle le principe du quantum fut explique. Une periode hero'ique, sans pareille dans Phis- toire de la science, la plus fructueuse et la plus passion- nante de la physique moderne. On ne trouve aucun do­ Les travaux de Niels Bohr peuvent etre divises en cument ecrit par Niels Bohr seul pour caracteriser cette trois periodes. Au cours de chacune d'elles, il exerca periode comme le document de 1913 pour la premiere une influence considerable sur le developpement de la periode. Bohr avait trouve une nouvelle methode de science moderne, de trois manieres differentes et a trois travail. II ne travaillait plus seul, mais en collaboration moments differents. La premiere periode s'etend de avec d'autres savants. Sa plus grande force etait de 1912, annee de sa rencontre avec Rutherford, a 1923. Elle rassembler autour de lui les physiciens les plus actifs, debute en 1913 avec la publication de ses travaux sur les plus doues, les plus intuitifs du monde. Pendant les orbites quantiques de 1'atome d'hydrogene. Bohr se cette periode, on trouve aux cotes de Bohr, dans son ce­ proposait d'expliquer les proprietes inconnues de lebre Institut de Physique theorique a Copenhague, des 1'atome en utilisant le concept des etats quantiques — un hommes comme Klein, Kramers, Pauli, Heisenberg, concept deja etabli par Planck et Einstein, et qu'il ap­ Ehrenfest, Gamow, Bloch, Casimir, Landau et d'autres plique a la structure de 1'atome. Je ne pense pas qu'il encore. C'est a ce moment et avec ces physiciens que existe dans la litterature de la physique un document les bases de la theorie des quanta furent jetees, que le qui engendra un si grand nombre d'idees nouvelles et principe d'incertitude fut enonce et diseute pour la pre­ duquel decoulerent autant de decouvertes. II est diffi­ miere fois, que Pantinomie particule-onde fut comprise cile de rencontrer un etre plus revolutionnaire. Son pour la premiere fois. Les problemes fondamentaux re- concept des etats quantiques de 1'atome etait selon latifs a la structure de la matiere furent eclaircis au toute evidence en contradiction totale avec le schema cours de discussions animees entre deux ou plusieurs du systeme planetaire que les experiences de Ruther­ personnes. C'est la que Pinfluence de Bohr se fit le ford avaient permis d'etablir. Mais les reponses aux mieux sentir. C'est la qu'il crea son «Kopenhagener principaux problemes fondamentaux etaient contenues Geist », style qu'il imposa a la physique — un style d'un dans cette contradiction meme. caractere tres particulier. On pouvait le voir, le premier entre ses egaux, travaillant, discutant, vivant avec un groupe de personnes jeunes, optimistes, enjouees et Ce document celebre marqua le debut d'une serie de enthousiastes, abordant les plus importants problemes nouvelles decouvertes. Au cours des dix annees qui de la nature avec un esprit d'attaque, un esprit libre suivirent sa parution, plusieurs phenomenes, jusqu'alors de tout lien conventionnel, avec une allegresse qu'il est inexpliques, trouverent leur place; la structure des difficile de decrire. Lorsque tres jeune, j'eus le privilege spectres des elements, le processus d'absorption et d'etre recu a l'lnstitut, je fus quelque peu surpris par d'emission de la lumiere, les causes qui regissent le les plaisanteries qui s'elevaient pendant les discussions, schema periodique des elements, la sequence curieuse et cela me sembla un manque de respect. Faisant part des proprietes des 92 differents elements atomiques. de mes sentiments a Niels Bohr, celui-ci me repondit : C'est la periode ou la qualite, la specificite des sub­ « Certaines choses sont tellement serieuses que l'on ne stances chimiques ont ete reduites a des donnees quanti- peut qu'en plaisanter ». tatives, au nombre d'electrons qui gravitaient autour de chaque atome. Tout cela reposait sur Phypothese des quanta appuyee par Bohr, qui n'etait alors qu'une Durant cette periode marquante de la physique, Bohr hypothese provisoire. Toutefois, les contemporains de et ses disciples penetrerent les secrets profonds de Puni- Bohr adopterent a la lettre les orbites quantifiers de vers. Les secrets de la Nature caches jusqu'a ce jour Pelectron permises ou non, bien que Bohr les ait mis en furent pcrces par les facultes mtelleetuelles de Phomme. La theorie des etats quantiques fut solidement etablie. champs. Ce document constitue un exemple typique de de meme que son integralite fondamentale et son indi- l'interet que Bohr temoignait a la teneur en physique visibilite qui pourtant echappent a l'observation ordi­ des theories mathematiques. naire d'une maniere particuliere, puisque le fait meme de l'observer ferait disparaitre les conditions de son existence. Bohr, dont les capacites penetrantes d'analyse La deuxieme direction dans laquelle etaient orientees contribuerent a un tel degre a eelaircir ces problemes, les recherches etait l'exploration de la partie la plus appela cette situation extraordinaire « la complemen­ secrete de l'atome, le noyau atomique. Anterieurement, tarity ». Ce mot met au defi une description imagee en on considerait que le noyau etait seulement la masse nos termes classiques habituels de physique, mais re- centrale de l'atome. Au cours de la troisieme periode, la vele du meme coup un monde beaucoup plus riche que structure du noyau suscita un vif interet, car un nom- notre experience classique ne nous permet de percevoir. bre toujours plus grand, de faits relatifs aux phenome- nes etroitement lies avec les parties les plus secretes de l'atome furent reveles. Ces faits etaient troublants a 1'origine, mais sous la conduite active de Bohr, on de- Lorsque les principes fondamentaux de la mecanique couvrit rapidement que l'univers du noyau etait gou- atomique furent etablis, il se revela possible de com- verne par les memes lois que la mecanique quantique. prendre et de calculer presque tous les phenomenes du Toutefois, dans ce cas, on se heurta a un probleme plus monde des atomes tels que les radiations atomiques la complexe en raison de 1'apparition de forces nouvelles liaison ehimique, la structure des cristaux, l'etat metal- et plus puissantes qui maintenaient l'unite du noyau, a lique et de nombreux autres. Avant cette epoque, le savoir les forces nucleaires. Lorsque le nombre conside­ monde se composait de nombreuses forces : electrique, rable des etats quantiques trouves dans les reactions adhesive, ehimique et elastique; des lors, toutes ces nucleaires poserent des problemes au monde des physi- forces se trouverent rassemblees en une seule : la force ciens, ce fut encore le concept de Bohr du « noyau com­ electromagnetique. En quelques annees seulement, les pose » qui permit de comprendre comment le grand bases d'une science des phenomenes atomiques furent nombre d'etats est lie a l'interaction forte entre les jetees et engendrerent les connaissances profondes que parties composantes du noyau. Les travaux de Bohr et nous possedons aujourd'hui. Jamais auparavant, tant ne l'esprit stimulant issus des discussions qui avaient lieu fut realise par si peu d'hommes en si peu de temps. a l'lnstitut de Bohr creerent une nouvelle science de la structure nucleaire qui permit de comprendre les phe- nomenes nucleaires et aussi un probleme deja ancien : les sources d'energie du soleil et des etoiles. Vint ensuite la troisieme periode des travaux de Bohr: les annees 1932 a 1940. L'annee 1932 fut importante pour le developpement de la physique : on enregistra la decouverte du neutron, du positron et de la radioacti­ Nous approehons maintenant de l'annee 1940, le debut vity artificielle, et le premier accelerateur de particules de la deuxieme guerre mondiale. Les episodes qui sui- entra en service. L'institut de Bohr, de renommee mon- vront dans la vie de Bohr sont, sous certains aspects, diale a l'heure actuelle, devint le centre des etudes de un temoignage encore plus important de la grandeur de physique theorique. Le probleme fondamental du quan­ cet homme. On ne peut les decrire en termes purement tum ayant ete resolu, les travaux de physique theorique scientifiques. Bohr n'etait pas seulement un grand continuerent dans deux directions. La premiere etait savant, il etait aussi un homme d'une sensibilite excep- 1'application des theories des quanta dans le domaine tionnelle a l'egard du monde qui l'entourait. Les rap­ des champs, electromagnetiques d'abord et nucleaires ports entre 1'homme et la science revetaient pour lui par la suite. Les travaux entrepris dans cette direction une importance capitale. II fut conscient, avant les ne sont pas encore termines a l'heure actuelle et de autres, du role decisif que la physique atomique jouait nombreux problemes fondamentaux relatifs a la struc­ et continuerait a jouer dans la civilisation et le destin ture des particules elementaires, qui sont a l'origine des de 1'homme — que la science ne pouvait pas etre isolee champs, ne sont pas encore resolus. Pendant cette pe­ du reste du monde. Par la suite, les evenements de riode, ces travaux se poursuivirent activement a Copen- l'histoire du monde soutinrent ce point de vue plus tot hague en etroite collaboration avec Pauli, Dirac et qu'on ne l'aurait pense. Dans les annees 1930 deja, une Heisenberg. Bohr, lui-meme, dans un document celebre breche s'ouvrit dans la tour d'ivoire de la science pure. publie en collaboration avec Rosenfeld, etablit la base Le regime nazi dirigeait l'Allemagne et un flot de physique des nouveaux concepts de quantification des savants se refugierent a Copenhague ou Bohr les re- cueillit et les secourut. II demanda a certains d'entre eux de rester avec lui ; pour James Frank, Hevesy, Placzek, Frisch et beaucoup d'autres, Copenhague fut un havre ou ils purent continuer leurs travaux scienti­ fiques. En outre, l'institut de Bohr etait le centre pour tous ceux qui s'interessaient a la science et qui avaient besoin d'aide, et plus d'un savant put obtenir un refuge — en Angleterre ou aux Etats-Unis — grace a l'assistance accordee personnellement par Bohr. Puis, vinrent les annees de guerre ; le Danemark fut occupe en avril 1940 par les Nazis ; la science pure etait morte. Bohr travaillait etroitement avec la resistance danoise. II refusa de collaborer avec les autorites nazies. II fut bientot oblige de quitter le Danemark, de fuir en Suede et arriva aux Etats-Unis en passant par 1'Angleterre.

Aux Etats-Unis, a Los Alamos, il se joignit a un groupe important de savants qui travaillaient alors a des recherches sur l'exploitation de l'energie nucleaire a des fins militaires. II ne se deroba pas a cet aspect le plus problematique des activites scientifiques. II aborda le probleme carrement comme une necessite ; mais parallelemerit, c'est son idealisme, son esprit de prevoyance et son espoir en la paix qui inciterent de nombreuses personnes de ce centre militaire a penser a 1'avenir et a preparer leurs esprits pour les travaux futurs. II nous aida a voir que, malgre la mort et la destruction, un avenir positif existait pour Phumanite que les connaissances scientifiques avaient transformee. II fit encore plus. II eut des contacts avec les hommes qui tenaient le pouvoir ; il vit Roosevelt, il vit Churchill. II fit une foule de choses qui, aujourd'hui, nous paraitraient naives. Nous etions d'ailleurs tous naifs lorsque nous pensions que la bombe serait abolie apres la guerre et qu'une paix durable serait etablie ; mais c'est cette naivete meme qui permet d'avoir Fes- poir et la force necessaires a un avenir pacifique. Nous devons etre conscients a 1'heure actuelle que c'est cette attitude ainsi que les discussions et les activites qui s'effectuerent grace a cet espoir qui ont contribue aux realites actuelles et peut-etre au fait que nous soyons encore vivants et capables de regarder 1'avenir avec confiance.

Puis vinrent les annees d'apres guerre : de 1945 a sa mort. La physique n'avait plus le meme aspect. La guerre avait fait ressortir, de maniere cruelle, que la Photo : M. Benarie, Tel-Aviv science est d'une importance immediate et directe pour chacun. Le caractere de la physique avait change. La physique devint une vaste entreprise : pour effectuer des recherches dans ce domaine, il fallait beaucoup de avaient engendre. Bohr en etait conscient et e'etait la monde et de grandes machines. Bohr admit ce change- raison pour laquelle il avait donne 1'appui de son enthou­ ment comme une suite logique des travaux qu'il avait siasme, de sa joie de vivre, de son attitude positive a entrepris avec ses amis. Les nouvelles idees qu'il avait ce nouveau developpement et en particulier a la nou­ emises depassaient la tour d'ivoire des universites dans velle poussee de la physique fondamentale en Europe. lesquelles certains auraient souhaite enfermer leurs Je me rappelle un exemple qui montre combien il connaissances. II comprit que de ces idees se develop- s'interessait aux activites du CERN. II y a un an en­ perait une grande realisation qui couvrirait tous les viron, Bohr avait ete prie d'apporter son concours a domaines des activites humaines ; il vit ainsi la neces­ la solution d'un probleme budgetaire. II vint au CERN sity de faire de la physique sur une grande echelle, et son aide fut precieuse pour regler la question ; apres voire sur une echelle internationale. Dans aucun la reunion qui dura toute la jour nee, et lorsque tous autre effort humain, les limites etroites imposees par etaient fatigues, il pria un des membres de Faccompa- les nationalites et la politique ne sont plus desuetes et gner pour une promenade ; il passa deux heures a ridicules que dans le domaine de la science. Bohr etait Geneve sous la pluie, expliquant ses vues sur la situa­ done toujours conscient du role important que la tion actuelle. On comprend difficilement comment un science doit jouer en creant un lien durable qui depasse homme de cet age pouvait avoir cette energie, cet inte- les limites nationales et politiques et en creant les ret enthousiaste de la vie ; e'etait toutefois une condi­ debuts d'une societe supranationale d'etres humains tion necessaire pour que se realisent ses travaux. II sur la terre. Voila pourquoi il s'occupa activement de la nous a donne cet accroissement immense de notre creation de centres internationaux de recherche scien- vision de la realite, qui fit trembler les fondations du tifique: le centre scandinave, NORDITA, a Copenhague monde, mais par ailleurs c'est son optimisme et son et enfin le centre dans lequel nous travaillons. C'est enthousiasme qui nous permettent de surmonter les grace a Bohr que le CERN existe. C'est la personna- difficultes auxquelles nous nous heurtons. lite de Niels Bohr, son influence et ses travaux qui ont permis de creer le Laboratoire. D'autres savants emi- Avec la mort de Niels Bohr, une epoque s'acheve — nents concurent 1'idee du CERN. Leur enthousiasme Fepoque des grands hommes qui creerent notre science. et leurs idees n'auraient pas suffi s'ils n'avaient pas Mais Niels Bohr lui-meme a participe a la creation des ete appuyes par un tel homme, qui ne se contentait bases pour la continuation future de travaux dans son pas seulement de les appuyer mais participait active­ esprit ; notre institution; le CERN, en est un temoi- ment a chaque stade important de la creation et du gnage. II nous contraint a continuer les travaux qu'il developpement de cette ceuvre, uni dans un commun souhaitait entreprendre. effort avec les autres pour discuter et s'inquieter de chaque detail. Voila ce qu'etait Niels Bohr. II est mort comme il a vecu. Deux semaines avant sa mort, il rentrait de vacances, entierement remis d'une La grandeur de cet homme se fait sentir dans cette legere attaque qu'il avait eue 1'an dernier ; ses mede- periode plus que dans toute autre. A soixante ans, Bohr cins lui avaient permis„ de reprendre son travail. II le etait pleinement conscient des nouveaux developpe- fit et s'en porta bien ; deux jours avant sa mort, le ments de la physique, de la nouvelle phase commencee vendredi, il presida meme une reunion de FAcademie dix ans plus tot, lorsque la possibility d'obtenir des fais- royale des Sciences du Danemark ; le dimanche, il avait ceaux de hautes energies permit d'aller plus loin que invite quelques amis chez lui. II etait heureux et en la structure du noyau et d'explorer la structure des bonne sante mais apres s'etre etendu pour quelques constituantes du noyau : le monde du proton et du neu­ moments de repos, il ne se reveilla pas. Qu'une telle vie tron. Cette nouvelle etape de la science n'est que la ait ete vecue et puisse Fetre a Fheure actuelle est un suite du courant immense que les travaux de Bohr grand encouragement pour nous tous •

Supplement a COURRIER CERN - Departement de ('Information du Public, CERN, Geneve 23 - Decembre 1962